The International patent application WO 03/094623, in the name of Valio Ltd, discloses a process for manufacturing a lactose-free milk product, comprising ultrafiltering, nanofiltering and reverse osmosis, followed by hydrolyzing the milk product. In the disclosed process a large amount of the original milk is lost.
U.S. Pat. No. 6,881,428 B2 discloses a method for producing milk with less than about 0.2% lactose by inter alia ultra filtration and ultrafiltration/diafiltration, wherein water is added upon subjecting the retentate to diafiltration.
US patent application 2005/0196508 discloses a sequential filtration process for producing a lactose-removed milk product. The obtained product is indicated to comprise 0.23% lactose.
The International patent application WO 2007/076873, in the name of Aria Foods amba, discloses a process for producing lactose-reduced milk comprising pH adjustment followed by ultrafiltration and nanofiltration; addition of water, and subsequent adjustment of pH. The amount of lactose in the final product is indicated to be 2.0%.